The present invention relates to thermal treatment techniques for semiconductor wafers, such as thermal oxidation treatment, diffusion treatment, CVD(Chemical Vapor Deposition) treatment, annealing treatment and the like.
Since in a typical semiconductor manufacturing process, a thermal treatment furnace is employed for conducting thermal treatments for objects, e.g., wafers, to be treated, such as thermal oxidation, diffusion, CVD, annealing and the like, it is necessary to provide a boat (or susceptor) loading apparatus for taking wafers in and out of a process tube of the furnace. As apparatus of this kind, an apparatus according to the boat loader method and one according to the paddle method are conventionally employed. However, according to the boat loader method, there is such a disadvantage that when a wafer jig is moved in the process tube, dust is generated from the contact portion and may produce wafer defects. On the other hand, according to the paddle method, there is such a disadvantage that since thermal treatment is conducted while a paddle is being inserted in the process tube, a temperature change may arise in the furnace, so that any thermal treatment cannot be conducted under a constant temperature.
Moreover, various apparatus have been proposed besides the above-mentioned two kinds of apparatus. However, since all of them are arranged such that the wafer jig is not moved out of the furnace until completion of the thermal treatment once the wafer jig is set inside the furnace, or they are sequentially controlled, such a problem may arise in high-temperature treatments, particularly such as diffusion treatment that the wafer jig, which is made of quartz, fuses with the process tube, which is also made of quartz, and they are united together, causing the wafer jig to be unable to move out of the furnace. Therefore, there is a limitation on intent to make the furnace temperature much higher in case of employing the wafer jig. Although such an apparatus has been devised as using a quartz fork adapted to take in and out the wafer jig without any contact with the inner wall of the process tube, still the problem of the above-mentioned fusing between the wafer jig and the process tube cannot be solved. If the fork is made to support the wafer jig while being placed inside the process tube so as to be prevented from contacting the process tube, such a problem arises that the fork may be deformed due to a high temperature, so that it cannot support the wafer jig in a normal way.
What mentioned above will be described hereinunder in greater detail.
As disclosed in Japanese Patent Laid-Open No. 129964/1978, the conventional boat loader method is such that, as shown in FIG. 1, a wafer jig (or boat or susceptor) 2 mounted with semiconductor wafers 1 is loaded into or unloaded from a process tube 5 of a diffusion furnace 3 while contacting with the process tube 5 by hooking a loading and unloading rod 4, capable of reciprocation in the extension direction of the diffusion furnace 3, at an end of the wafer jig 2. According to the boat loader method, however, since the wafer jig 2 is loaded or unloaded while contacting with the process tube 5, they rub together and may cause the reactant powder attached to the inner wall of the process tube 5 to separate therefrom and attach to the surfaces of the semiconductor wafers 1. The attached substance may produce such defects as projections and pinholes in the films formed on the semiconductor wafers 1 through the thermal treatment, causing the characteristics of the thin films to be deteriorated as well as the production yield and reliability of semiconductor devices such as IC, LSI are lowered.
On the other hand, as disclosed in Japanese Patent Laid-Open No. 12996/1978, the paddle method is such that, as shown in FIG. 2, a roller 6b is provided at an end of a paddle (long rod) 6 having a wafer-receiving part 6a, and the paddle 6 mounted with the wafers 1 in the receiving part 6a is loaded into or unloaded from the process tube 5 of the diffusion furnace so as to move along the process tube 5. According to the paddle method, however, since a diffusion treatment is conducted while the paddle 6 is being loaded in the process tube 5, the heat inside the process tube 5 is taken by the paddle 6, causing a change in the temperature in the process tube 5, so that any diffusion treatment cannot be performed under a constant temperature, and moreover, since the process tube 5 and the roller 6b are under a contact state, dust is generated in the process tube 5 although the amount of the dust generated is smaller than that in the above-mentioned boat loader method.
Furthermore, as disclosed in Japanese Patent Laid-Open No. 36129/1981, such a thermal treatment apparatus as illustrated in FIG. 3 is conventionally employed when wafers are subjected to thermal treatment such as diffusion and oxidation. The apparatus generally comprises a boat transfer part 7, a gas discharge part 8, a furnace body 9 and a gas supply part 10. A plurality of process tubes 11 each having a horizontal axis are vertically disposed in the furnace body 9, and adapted to be heated to a desired temperature by means of a heater or the like, not shown. Moreover, the extended portion of each of the process tubes 11 is opened at the gas discharge part 8 so that a boat, described hereinafter, can be reciprocatively moved in and out of each the process tubes 11.
On the other hand, a boat loader 12 is disposed in the boat transfer part 7, corresponding to the extension line of each of the process tubes 11. Although, FIG. 3 illustrates only the uppermost boat loader, each boat loader 12 comprises: a boat driving part 14 having a portion projected from a driving mechanism, not shown but disposed in the cover of the boat transfer part 7, to the outside of the cover through a groove 13 and adapted to reciprocate in the axial direction of the corresponding process tube 11; and a boat 15 disposed along the axial extension line of the process tube and having the tail end attached to the boat driving part 14 so as to move in or out of the process tube in accordance with the movement of the boat driving part 14. Semiconductor wafers 16 to be subjected to a thermal treatment are held at the top end of the boat 15.
Treatment in the thermal treatment apparatus such as described above is conducted according to the following procedure: As shown in FIG. 4, after a mounting jig 17 for mounting semiconductor wafers is placed on the top end of the boat 15 and the semiconductor wafers 16 are held by the jig, the boat driving part 14 is actuated so that the boat 15 is entered into the process tube 11. When the boat 15 is entered to a given position, the whole or the top end of the boat 15 is slightly moved downward, thereby allowing the mounting jig 17 to be placed on the bottom surface inside the process tube. Thereafter, the boat 15 is moved backward and drawn out of the process tube 11, thereby allowing only the mounting jig 11 and the semiconductor wafers 16 to be left inside the process tube, and then the opening of the process tube is capped to conduct, what is called, a thermal treatment. The semiconductor wafers having completed the thermal treatment are placed on the top end of the boat 15 entered into the process tube again, together with the jig 17, and unloaded from the process tube by drawing out the boat.
Accordingly, in the thermal treatment, it is necessary to move the boat 15 in and out of the process tube 11 twice in order to perform one thermal treatment, and moreover, there is a need for an operation to cap the opening of the process tube after the semiconductor wafers are set inside the process tube. Therefore, there are such problems that the time needed for the whole process of the thermal treatment becomes longer and it becomes difficult to automatize these operations in the process.
In addition, according to such a treatment method as described above wherein the semiconductor wafers 16 loaded in the process tube 11 are left therein together with the mounting jig 17, the jig 17 must be provided with support legs 18 which abut against the bottom surface inside the process tube when the boat 15 is slightly moved downward, as shown in FIG. 5 illustrating the sectional structures of the boat 15 and the jig 17 respectively, and moreover, each of the support legs 18 must be formed so that the lower end thereof is projected lower than the bottom surface of the boat 15. Consequently, the lower end of each of the support legs 18 easily interferes with the inner surface of the process tube 11 when the semiconductor wafers are loaded or unloaded, so that there are possibilities of damage to the support legs 18 and the inner surface of the process tube 11. If, especially, the inner surface of the process tube is damaged, cuttings may mix with a gas in the process tube and prevent the thermal treatment from being normally conducted. Therefore, it is conventionally necessary to design the inside diameter of the process tube to be sufficiently large, and this is an obstacle to miniaturization of such an apparatus as mentioned above wherein the process tubes each having a horizontal axis are vertically disposed.
Further, there is such another thermal treatment apparatus as described hereinunder, as disclosed in Japanese Patent Laid-Open No. 36129/1981.
FIG. 6 shows an arrangement of the essential part of the another conventional diffusion apparatus, i.e., an arrangement of a boat loader. Since each of a furnace body having process tubes, a gas discharge part and a gas supply part has the same arrangement as shown in FIG. 3, the description thereof is omitted. As shown in the figure, a boat driving part 14A of a boat loader 12A has a moving plate 20 capable of reciprocating on two guides 19 provided on a base 24 in the axial direction of the proces tube, the moving plate 20 being able to be reciprocated by rotating a feed screw 21 screwed into the moving plate 20 by means of a motor 22. In addition, a portion of the moving plate 20 is projected to the outside of a cover through a groove 14 formed in the cover, forming a boat securing plate 23 (see FIG. 3).
The tail end of a boat 15A formed into a substantially cylindrical shape is secured to the securing plate 23 by means of two belts 24, while the top end of the boat 15A is supported by means of a roller 25 provided on the process tube side so that the boat 15A can be moved in and out of the process tube in accordance with the movement of the securing plate 23. The boat 15A is formed from a heat-resisting member such as quartz, and as shown in FIG. 7 which illustrates the side configuration, a substantially upper half of the cylinder is cut at the top end portion, which is sealed by means of a bottom plate 26 and an end plate 27, thereby to form a mount 29. The mount 29 has baffles 30 provided at both ends and is adapted to be capble of placing a mounting jig 17A for mounting semiconductor wafers 16 between the baffles 30. It is to be noted also that the jig 17A is placed on the mount 29 while supporting the semiconductor wafers 16 fitted in the notches formed in parallel stems respectively and does not have such support legs as shown in FIG. 5.
On the other hand, a tubular inner cap 32 filled therein with a heat-insulating material 31 such as glass fiber or the like is received in the hollow inside the boat 15A at a substantially central portion thereof, precisely speaking, at such a portion that the boat 15A faces to the opening of the process tube 11, shown by imaginary lines in FIG. 7, when entering thereinto. Similarly, a substantial saddle-shaped outer cap 34 filled therein with a heat-insulating material 33 is fitted on the upper part of the outer periphery of the boat 15A. These inner and outer caps 32, 34 are adapted to close the opening of the process tube in cooperation with each other when the boat 15A enters into the process tube.
The operation of the above-mentioned apparatus will be described hereinunder.
After the mounting jig 17A is placed on the mount 29 at the top end of the boat 15A and moreover the semiconductor wafers 16 are mounted thereon, the motor 22 is driven. Consequently, the feed screw 21 allows the moving plate 20 and the securing plate 23 to move toward the process tube 11 along the guides 19, causing the boat 15A to enter into the process tube from its top end. While being supported by the roller 25, the boat 15A is entered into the process tube 11 along the slightly lower side thereof. Stopping the boat 15A when the semiconductor wafers 16 are inserted to a given position allows the inner and outer caps 32, 34 having just moved to the position of the opening of the process tube to close the opening in cooperation with each other. Thereby, if the process tube is heated under this condition and moreover a thermal treatment is conducted while a gas is being supplied according to circumstances, it is possible to perform the thermal treatment while the inside of the process tube is kept under a thermally sealed state. On completion of the thermal treatment, the boat 15A is drawn out of the process tube and the semiconductor wafers 16, together with the jig 17A, are brought down from the boat, and semiconductor wafers to be subsequently treated are placed together with the jig, thereby to make it possible to conduct the subsequent thermal treatment in a similar manner to that described above.
However, in each of the apparatus shown in FIG. 3 through FIG. 5 and FIG. 6 thru FIG. 7, since the wafer jig is loaded or unloaded while the jig and the process tube are contacting with each other, they rub together and may cause the reactant powder attached to the inner wall of the process tube to separate therefrom and attach to the surfaces of the semiconductor wafers. The attached substance may produce defects such as projections and pinholes in the films formed on the semiconductor wafers by means of the thermal treatment, so that the thin film characteristics are deteriorated and the production yield and reliability of semiconductor devices such as IC, LSI or the like are lowered.
Moreover, there is such a disadvantage that since the process tube and the roller are contacted with each other, dust may be generated inside the process tube and curled up.